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Developments in pop-up satellite archival tags (PSATs) have greatly improved scientific understanding of the postrelease survival, behav-ior, and movements of marine ver-tebrates—animals from which it is not always practical to physically recover tags to obtain data (Arnold and Dewar, 2001; Graves et. al. 2002). PSATs take measurements of physical conditions (e.g., temperature, pres-sure, light level) while attached to study animals, independently detach at predetermined times, float to the surface, and transmit data to orbiting satellites of the Argos system. Owing to the mass and size of older tags (~65 g), PSAT deployments have histori-cally been limited to large pelagic marine vertebrates such as billfishes, tunas, sharks, and sea turtles. Recent miniaturization of tag components has led to the development of a new gener-ation of PSATs that are 33% smaller, thus enabling the collection of high-resolution time-series data for infer-ences regarding short-term fate and habitat use by increasingly smaller species, including many estuarine and coastal fishes.

To evaluate the utility of the new generation of smaller PSATs for stud-ies of estuarine and coastal fishes, we deployed ten tags on large, coastal, migratory striped bass (Morone saxa-tilis) caught on live baits rigged on two hook types in the winter recre-ational fishery off coastal Virginia and North Carolina. Although small-

Use of pop-up satellite archival tag technology to study postrelease survival of and habitat use by estuarine and coastal fishes: an application to striped bass (Morone saxatilis)

John E. Graves (contact author)

Andrij Z. Horodysky

Robert J. Latour

E-mail address for contact author: [email protected]

Virginia Institute of Marine ScienceCollege of William and MaryRoute 1208 Greate Rd.Gloucester Point, Virginia 23062

Manuscript submitted 6 December 2008.Manuscript accepted 24 April 2009.Fish. Bull. 107:373–383 (2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

Abstract—Pop-up satellite archi-val tags (PSATs) have been used to study movements, habitat use, and postrelease survival of large pelagic vertebrates, but the size of these tags has historically precluded their use on smaller coastal species. To evaluate a new generation of smaller PSATs for the study of postrelease survival and habitat use of coastal species, we attached Microwave Telemetry, Inc., X-tags to ten striped bass (Morone saxatilis) 94–112 cm total length (TL) caught on J hooks and circle hooks during the winter recreational fishery in Virginia. Tags collected tempera-ture and depth information every five minutes and detached from the fish after 30 days. Nine of the ten tags released on schedule and eight trans-mitted 30% to 96% (mean 78.6%) of the archived data. Three tags were physically recovered during or after the transmission period, allowing retrieval of all archived data. All eight striped bass whose tags trans-mitted data survived for 30 days after release, including two fish that were hooked deeply with J hooks. The eight fish spent more than 90% of their time at depths less than 10 m and in tem-peratures of 6–9°C, demonstrated no significant diel differences in depth or temperature utilization (P>0.05), and exhibited weak periodicities in vertical movements consistent with daily and tidal cycles.

er PSATs provide opportunities to investigate smaller species, coastal and estuarine fishes and the charac-teristics of their habitats present spe-cial challenges for PSAT deployments. First, many coastal species associate with physical habitat structures in which the tags could become entan-gled, possibly resulting in premature release of the tag. Secondly, many coastal species aggregate, providing opportunities for conspecifics or other species to interact with the tag, pos-sibly causing premature release or damage to the PSAT. Finally, because coastal species are found near shore, there is an increased probability that a released (transmitting) PSAT will wash ashore during the transmission period, potentially reducing the qual-ity and quantity of subsequent data transmissions. On the other hand, the increased probability of beaching dur-ing data transmission may provide researchers opportunities for directed tag recovery.

A second goal of this study was to gain insights into the postrelease survival of striped bass released from recreational fishing gear dur-ing the winter prespawning aggrega-tion near the mouth of Chesapeake Bay. Striped bass are a highly prized recreational gamefish, providing over $300 million to the U.S. economy and over $60 million to Virginia annu-ally (Kirkley and Kerstetter, 1997; Richards and Rago, 1999). Manage-ment regulations, such as seasonal

374 Fishery Bulletin 107(3)

bag and size limits, have resulted in the release of over 90% of the striped bass caught by recreational anglers (Van Winkle et al., 1988). Current recreational postrelease mortality estimates for striped bass range between 3% and 67%, and a value of 9% is currently used in population assessments for the Chesapeake Bay stock (Diodati and Richards, 1996). However, previous studies have generally been conducted in fisheries and environmental conditions very different from those near the mouth of Chesapeake Bay during the winter months (Table 1).

A third goal of this study was to determine habitat use by coastal migrant striped bass during the winter prespawn aggregation in the coastal sea along Virginia. Habitat use by juvenile striped bass within estuarine and riverine waters has been fairly well studied (Tupper and Able, 2000; McGrath, 2005), as have the move-ments of adults during upriver spawning migrations (Carmichael et al., 1998). Little is known about the depth and temperature use or short-term movements of adult striped bass in winter prespawning aggrega-tions along the U.S. Mid-Atlantic coast, despite the importance of Chesapeake Bay to the coastal migrant population. The Chesapeake Bay stock is thought to be the most productive along the Atlantic coast, serving as a major source of coastal recruits and accounting for >90% of Atlantic coastwide landings in some years (Kohlenstein, 1981; Richards and Rago, 1999; Secor, 2000). Identifying habitat characteristics and patterns of habitat use by coastal migrant species in areas of ag-gregation are necessary for effective current and future management efforts (Carmichael et al., 1998; Conrath and Musick, 2008).

Materials and methods

The X-tag high rate archival tag (X-tag, Microwave Telemetry, Inc., Columbia, MD) used in this study is slightly buoyant, and weighs 40 g in air. The body of the tag contains a lithium composite battery, a micropro-

Table 1Summary of published postrelease survival experiments using J, treble, and circle hooks conducted on striped bass (Morone saxatilis) released from the recreational fishery. F=freshwater, S=saltwater followed by the state abbreviation. Hook types are: J (straight-shank J hook), C (circle hook), and T (treble hook). For release mortality, estimates are for artificial lures (L), live bait (B), J hooks (J), or circle hooks (C).

Source Water type and region Season Hook Bait type or lure Release mortality

Harell (1988) F Winter, summer J Live bait, lures L: 15.6%, B: 30.7% Hysmith et al. (1993) F: TX Winter, summer J Live bait, lures 38%Diodati and Richards (1996) S: MA Summer J Live bait, lures 3–26%; mean 9%Nelson (1998) F: NC Spring J, T Live baits, lures 6–27%: mean 6.3%Bettoli and Osborne (1998) F: TN Winter, summer J , T Live baits, lures 14–67%Lukacovic and Uphoff (2002) S: MD Summer J Natural baits J: 9.1% C C: 0.8%Millard et al. (2003) F: NY Spring J Natural baits 8–18%

cessor, a pressure sensor, a temperature gauge, a light sensor, and a transmitter, all encased within a carbon fiber housing. Flotation is provided by a spherical resin bulb embedded with buoyant glass beads and the tag can withstand pressure equivalent to a depth of 2500 m. This tag model was programmed to record and archive a con-tinuous time series of temperature, light, and pressure (depth) measurements approximately every five minutes for 30 days. The tags can transmit depth measurements at intervals of approximately 1.3 m and temperature in increments of 0.17°C. Not having prior information on the time course or range of vertical movements of striped bass overwintering off the mouth of Chesapeake Bay, we chose not to activate an optional feature that provides for early tag release in the case of a mortality which is inferred if the tag remains at constant depth (±1.5 m) for four days. The X-tags were equipped with Satellite in ViewTM software that increases battery life and data recovery by restricting transmissions to times during which there is a high likelihood that the Argos satellite will pass above the horizon.

Striking a balance between availability and size of striped bass in the winter recreational fishery off the mouth of Chesapeake Bay, we arbitrarily set a mini-mum length threshold for tagging of 94 cm total length (TL). Striped bass in this size range are sexually ma-ture coastal migrants (Dorazio et al., 1994) that weigh 8 kg or more (Secor, 2000) and were considered to be of sufficient size to carry the X-tag.

Striped bass were caught by using live eels (Anguilla rostrata) as bait on 13.6-kg test sportfishing tackle with 1.2-m leaders of 36.3-kg test line. Five striped bass were caught on J hooks (Gamakatsu Octopus, size 7/0, no offset), and five on circle hooks (Gamakatsu Octopus Circle, size 7/0, no offset). Fish were netted and brought on deck where the hook location was noted, the hook removed, total length measured, and the PSAT attached before the fish was returned to the water (air exposure time less than two minutes).

PSATs were attached to striped bass by an assembly composed of 16 cm of 182-kg test monofilament fishing

375Graves et al.: Use of archival tags to study postrelease survival of and habitat use by estuarine and coastal fishes

Figure 1X-tag (Microwave Telemetry, Inc., Columbia, MD) attached to a striped bass (Morone saxatilis). The nylon intramuscular tag anchor was inserted approximately 5 cm towards the dorsal midline, an area where the anchor had a high likelihood of securely interlocking with the pterygiophores supporting the dorsal fin spines.

line (Momoi Fishing Co., Ako City, Japan) attached to a large, hydroscopic, surgical-grade nylon intramuscular tag anchor according to the method of Graves et al. (2002). Attachment assemblies were implanted with a 5-cm stainless steel applicator attached to a 0.3-m tagging pole that was inserted behind a scale approxi-mately 5 cm deep into a target region approximately 6 cm posterior to the origin and 5 cm ventral to the base of the dorsal fin (Fig. 1). In this region, the nylon anchor can pass through and potentially interlock with pterygiophores supporting the dorsal fin well above the coelomic cavity containing visceral organs (Graves et al., 2002).

Data analyses

Net movement was calculated as a minimum straight line distance (MSLD) traveled between coordinates of initial tagging and coordinates of the first reliable sat-ellite transmission by using Argos location codes 1, 2, or 3 (Horodysky et al., 2007). Archived and transmitted point measurements of depth and temperature recorded by PSATs were summarized in 5-m and 1°C interval histograms. Data sets were truncated to remove records before tagging and after PSAT pop-up.

To assess potential diel differences in habitat utiliza-tion, mean depths and temperatures were generated for each diel period (day, night) of each tracking day (n=30) for each of the eight striped bass. Diel period designa-tions were based on times of local sunrise and sunset;

crepuscular periods (30 minutes on either side of dawn and dusk) were eliminated from all diel analyses. Diel differences in the depth and temperature means were assessed separately with linear mixed effects models of the following form (Pinheiro and Bates, 2004):

Ypi p i pi= + + +µ τ α ε , (1)

where μ = the overall mean depth or temperature; τp = the fixed effect of diel period p; αi = the random effect due to individual fish; and εpi = error terms.

Application of linear models requires satisfying three assumptions: independence and normality of the response within and among samples, and homogeneity of vari-ances among all levels of the fixed effects (Underwood, 2002). However, PSAT data constitute repeated noninde-pendent observations within individual fish and may fail to satisfy the assumptions of normality and homogeneity of variance. Accordingly, a repeated measures form of Equation 1, including a Box-Cox transformation of the depth and temperature data, rectified these problems in the striped bass data. To characterize the within-individual autocorrelation, several candidate covariance structures were fitted to the transformed depth and temperature data, and the appropriate structure was selected by using Akaike’s information criterion (AIC):

AIC L p= − +2 2ln( ˆ ) , (2)


Table 2Hook type, hooking location, release date, fish size, PSAT data recovery, and net movement data for striped bass (Morone saxati-lis) caught on live eels (Anguilla rostrata) in the winter recreational fishery off the coast of Virginia and North Carolina. Starred (*) data recovery percentages indicate instances where PSATs were physically recovered, allowing a full download of all archived data. Minimum straight line displacements (MSLDs) were calculated in nautical miles (nmi) from the coordinates of tagging to the coordinates of first reliable satellite contact (Argos location code 1, 2, or 3).

Fish Hook type Hooking location Date released Total length (cm) Data recovery (%) MSLD (nmi)

1 J Deep 26 Jan 08 94.0 90 29.92 J Upper jaw 26 Jan 08 94.0 100* 56.33 C Jaw corner 26 Jan 08 96.5 87 27.84 C Upper jaw 27 Jan 08 111.8 100* 34.35 C Jaw corner 27 Jan 08 94.0 90 58.66 J Deep 2 Feb 08 96.5 96 12.57 C Upper Jaw 2 Feb 08 104.1 30 27.18 J Upper Jaw 2 Feb 08 101.6 100* 32.5

where L̂ = the estimated value of the likelihood function at its maximum; and

p = the number of estimated parameters (Burn-ham and Anderson, 2002).

We performed fast Fourier transform (FFT) analy-ses to assess any periodicities inherent in the time series of the three recovered tags for which 100% of the archived data were obtained. FFT approximates a function composed of sine and cosine terms from a time series (Chatfield, 1996) and is particularly well suited to analyzing high-resolution data sets resulting from archival tagging studies (Graham et al., 2006; Shepard et al., 2006). The influence of periodic components in a time series is indicated by the magnitude of the cor-responding spectral peak in a periodigram (Shepard et al., 2006). Spectral components of fractional periodici-ties (i.e., part of a tidal cycle, moon phase, etc.) occur-ring before and after the tag deployment duration can interfere with each other, generating frequency peaks that do not represent meaningful behavioral period-icities (Shepard et al., 2006). We therefore applied a Hamming window to the depth records of each of the three striped bass to reduce the effects of such adja-cent spectral components (Oppenheim and Schafer, 1989). All statistical analyses were performed with the software package R, vers. 2.7.1 (R Development Core Team, 2008).

Results

Ten striped bass, ranging in size from 94 to 112 cm TL (mean=96.5 cm), were caught on live eels rigged with circle or J hooks in coastal waters (<20 m depth) of Virginia and North Carolina during late January and early February 2008 (Table 2). Fight times ranged from 1 min 10 sec to 5 min 30 sec (mean=2 min 16 sec). All five fish caught on circle hooks were hooked

externally, either in the upper jaw or the corner of the jaw. Two of five fish caught on J hooks were hooked deeply and the other three were hooked externally. Hooks were removed from all fish before they were tagged and released.

Eight of the ten PSATs popped up on schedule and transmitted data that were received by satellites of the Argos system. A single, weak transmission was received from one of the two remaining tags on the day it was scheduled to release, and no transmis-sions were received from the other PSAT. The tags had sufficient battery power to transmit data for ap-proximately 30 days, and during that time three of the eight reporting PSATs washed ashore. Two of these tags (from fish 2 and 4) were physically recov-ered while transmitting data. Transmissions from the third tag (fish 7) ceased when the PSAT washed ashore four days after surfacing; this tag was not recovered. A fourth tag (fish 8) remained adrift dur-ing its transmission period and subsequently washed ashore north of Cape Hatteras, NC, where it was recovered by a recreational angler.

Data recovery rates varied among the eight trans-mitting tags. All of the archived data were manually downloaded from the three tags that were recovered after having washed ashore. For the four tags that remained adrift during the transmission period and not subsequently recovered (fish 1, 3, 5 and 6), data recovery rates were high, ranging from 87 to 96%. The PSAT from fish 7 surfaced just off the seaside of the Eastern Shore of Virginia and washed ashore on Parramore Island after four days, at which time transmissions ceased to be received. During the four-day transmission period, 30% of the archived data were recovered from this tag.

From a visual inspection of depth and temperature data we inferred that all eight striped bass with re-porting tags, including the two fish that were deeply hooked with J hooks, survived for 30 days after re-


lease. Each f ish exhibited multiple vertical move-ments in the water column throughout the 30-day tagging period (Fig. 2). Inferences of survival based on depth and temperature data were also support-ed by calculations of net movement (Graves et al., 2002). Minimum straight line displacements for the eight striped bass ranged from 12.6 to 58.6 nautical miles (nmi; 23.3–108.5 km), with a mean of 34.9 nmi (64.6 km; Fig 3). During the 30-day tagging period, three individuals (fish 2, 4, and 5) left coastal waters and entered Chesapeake Bay, presumably initiating spawning migration.

Depth and temperature data archived by the eight transmitting X-tags demonstrated that coastal migrant striped bass spent >90% of their time in the upper 10 m of the water column in temperatures of 6–9°C (Fig 4). Two striped bass (fish 2 and 5) entered warm tem-peratures (~15°C) at approximately the same time on the same date. These individuals, tagged on different days in North Carolina waters, may have moved east-ward to a warm core eddy confirmed by satellite tem-perature imagery for 7 February 2008 (http://marine.rutgers.edu/cool/sat_data, accessed May 2008). It is also possible that these fish instead moved into shallow

Figure 2Depth (left axis, open black symbols) and temperature (right axis, closed grey symbols) time series from Microwave Telemetry X-tags deployed on eight large coastal migrant striped bass (Morone saxatilis) from January through March 2008. Tags for fish 2, 4, and 8 were recovered and represent the full 100% downloaded data streams.


Figure 3Minimum straight line displacements (MSLD) in nautical miles (nmi) of eight large coastal migrant striped bass (Morone saxatilis) caught on recreational fishing gear and tagged with Microwave Telemetry X-tags from January through March 2008. Arrow bases (circles) indicate location of fish tagging and release, arrow tips denote the first point of contact with transmitting tag after release from the fish.

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coastal or estuarine waters warmed by unseasonable temperatures (~18°C) on 7 February 2008.

Despite the daily variability in the tracks of indi-viduals, repeated-measures linear mixed-effects models yielded no significant diel differences in striped bass depth or temperature utilization (P>0.05). The best fitting model for both depth and temperature data was the autoregressive moving average (ARMA) covariance structure.

Fast Fourier transform periodigrams of the three recovered tags revealed weak periodicities in vertical movements consistent with one cycle per day (i.e., 24 hours), and weaker behaviors consistent with two and three cycles per day (i.e., 12 and 8 hours, respective-ly; Fig. 5). All three periodigrams had large spectral peaks near zero, a consequence of standardizing the depth data by the average depth; main spectral peaks follow this initial clustering (Shepard et al., 2006). The main spectral peaks were identified both with and without the Hamming window, and thus were not attributed to artifact. It is unclear if the periodicities of approximately 12 hours and 8 hours represent spe-cific behavioral cycles or harmonics that result from nonsinusoidal behavior (Chatfield, 1996).

Discussion

The primary goal of this study was to evaluate the per-formance of a new generation of smaller PSATs on estua-rine and coastal species in the nearshore environment. The larger, older models of PSATs have been deployed on coastal elasmobranchs (Grusha, 2005; Conrath and Musick, 2008). As comparatively smaller coastal and estuarine fishes become candidates for these smaller tags, researchers may wish to consider the minimum size at which drag and lift forces acting on the PSAT impact behavior and survival (Grusha and Patterson, 2005). From the movements of fish and the lack of observed mortalities, we conclude that striped bass of ~1 m TL length appear to be of sufficient size to carry the X-tag.

At the outset of this study we were concerned with the potential for premature release of PSATs because of entanglement in physical structure, fish-tag inter-actions that would result in premature release or tag damage, and the likelihood that tags would effectively transmit the archived data from nearshore waters. The lack of prematurely released tags in this study confirms that fouling or interactions with structure


Figure 4Time-at-depth (A) and time-at-temperature (B) histograms from Microwave Telemetry X-tags deployed on eight large coastal migrant striped bass (Morone saxatilis) from January through March 2008. Each fish was given equal contribu-tion. Error bars are ±1 standard error.

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were not problematic for striped bass; however, the applicability of these results to other struc-ture-associated species is not known. Premature release of PSATs has been noted in many stud-ies and may become more prevalent with longer deployment times because of attachment methods and increased potential for fish-tag interactions (Domeier et al., 2003; Conrath and Musick, 2008; Graves and Horodysky, 2008). The selection of a specific attachment method and an appropriate release time will depend on the species studied and research objectives of the study (e.g., postrelease mortality, movement, or habitat use).

Fish-tag interactions present challenges for all PSAT studies and may occur as predation of a tag mistaken for a prey item or predation of an indi-vidual carrying a tag. Both outcomes are extremely difficult to quantify and compromise study objec-tives. In schooling piscivorous fishes, such as adult striped bass, predation of PSATs is more likely than predation of the study individuals. We cannot discount that our nonreporting and weakly trans-mitting tags may have been victims of tag preda-tion; it is often impossible to discern between tag predation and tag failure. However, it is unlikely that mortality of a tagged striped bass would result in a nonreporting tag because the PSAT should surface from a dead carcass after 30 days. The predation of live individuals by elasmobranchs, as well as the scavenging of dead fish carrying PSATs by elasmobranchs, was inferred in previ-ous studies (Kerstetter et al., 2004; Kerstetter and Graves, 2008). In these instances, the PSATs were not compromised during ingestion and success-fully transmitted after being regurgitated, but it is likely that damage during such events may be a cause of PSAT nonreportings.

The success of studies where PSAT technology is used depends upon on the quality and quantity of the archived data that are transmitted from the tag to the Argos satellite system. Reception of PSAT transmissions is maximized when the tag antenna is unobstructed and above the surface of the water in a vertical position. In our study, we obtained at least 87% of the data from tags that re-mained adrift for the entire data transmission period. There is an increased probability that tags attached to estuarine and coastal fishes will wash ashore during the transmission period that typically lasts about 30 days. Tags beach in a horizontal position which may result in decreased signal reception, especially if an-tennae are submerged in water or fouled with algae or other debris.1 Beached tags in this study transmitted 30–90% of their data. In the case of the tag attached to fish 7, which beached after only four days of trans-mission and ceased communicating with the satellite shortly thereafter, the transmission of over 3000 data points provided more than sufficient information to infer survival and investigate habitat use by that indi-vidual. The random transmission of data packets (nine

1 P. Howey. 2009. Personal commun. Microwave Tele- metry, Inc., 8835 Columbia 100 Parkway, Suites K & L, Columbia, MD 21045

consecutive time points) by the X-tags during times when a satellite of the Argos system is likely above the horizon generally results in a rapid accumulation of data during the first week of the thirty-day trans-mission period (Fig. 6).

The two tags that were recovered while still trans-mitting (fish 2, 4) were carried by fish that moved from coastal waters into the mainstem of Chesapeake Bay. We timed the X-tags to release while striped bass were in coastal or estuarine waters before their annual spring spawning migration to freshwater. The release mechanism on the PSAT, which operates by electrolysis, requires a >5 ppt salinity to function,1 which necessi-


Figure 5Fast Fourier transform periodigrams for depth data from three recov-ered Microwave Telemetry X-tags (fish 2, 4, and 8) deployed on eight large coastal migrant striped bass (Morone saxatilis) from January through March 2008 and physically recovered. Periods of the main spectral peaks found with the raw data and the Hamming window are identified with open circles and labeled in hours.

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tates consideration when dealing with anadromous or catadromous fishes.

PSAT deployments in estuarine and coastal waters will likely have higher tag-to-human interaction rates than those deployed in oceanic waters, and will poten-tially lead to greater rates of tag recovery. However, to realize these potential benefits, which may be consider-able in highly populated regions, the incentive (finan-cial, material, or otherwise) for returning a recovered tag must be sufficient (Pollock et al., 2001). Historically, tag-recovery rates in PSAT studies have been very low. However, Kerstetter and Graves (2008) recently re-ported recoveries of 4 of 17 PSATs (23.5%) attached to sailfish released from pelagic longline operations in the Gulf of Mexico, south of Key West, FL, and all recover-ies came from the heavily used beaches of southeast Florida. Recovery of PSATs can further be aided by the

use of radio antennae if tags are transmitting1; tags in dense cover can also be located by a metal detector at close range (<0.5 m: A. Horodysky, personal obs.). Tag recovery is beneficial not only because it is possible to obtain 100% of the archived data from the PSAT, but recovered tags can be refurbished for approximately 20% of the cost of a new tag.

A second objective of this study was to assess po-tential differences in postrelease survival of striped bass caught on live eels rigged with J hooks and circle hooks in the winter recreational fishery. Although the limited sample size precluded statistical comparisons, tags from all eight fish returned data that indicated survival. Circle hooks reduce deep-hooking, hook-in-duced trauma, and mortality of many fishes (Cooke and Suski, 2004; Horodysky and Graves, 2005), including that of striped bass (Table 1). Previous research has

demonstrated a high mortality of striped bass deep-hooked with J hooks and addi-tional and interactive stress-related mortal-ity of larger striped bass caught in warm, low-salinity waters (>20°C, <10 ppt) and handled in still higher air temperatures (>30°C) (Wilde et al., 2000; Lukacovic and Uphoff, 2002). Handling exhausted fish in warmer air can further raise basal meta-bolic rate, exacerbating oxygen demand and blood chemistry problems (Gingerich, et al., 2007) while simultaneously reducing the gill surface area because of the physical collapse of the gill lamellae and adhesion of the gill filaments (Cooke et al., 2002). We observed 100% survival of tagged fish, in-cluding two animals deeply hooked with J hooks, caught in cool, high salinity waters (<10°C, >25 ppt), and handled briefly (<2 minutes) in cool air temperatures (<18°C). Although further work is still needed, the results of these studies indicate that the winter recreational fishery in Virginia may not be a significant source of postrelease mortality for striped bass and that release mortality of this species likely varies tem-porally and spatially because of physiologi-cal stressors.

A third objective of this study was to gain insights into habitat use by striped bass overwintering near the mouth of Chesapeake Bay. Net displacements of the eight fish over the 30-day tagging period were limited, averaging less than 35 nmi (64.8 km). We did not use geolocation al-gorithms based on light and sea surface temperature data to infer horizontal move-ments of fish within the 30-day tagging period because the mean displacements over the 30 days were substantially less than the root mean square (RMS) errors associated with daily estimates of geolo-cation. Under optimal condition, such as


clear pelagic seas, RMS errors associated with geolocation estimates based on light and sea surface temperature data exceed 100 km (Teo et al., 2004; Nielsen and Sibert, 2007), and the hyperdynamic light conditions characteristic of turbid, tidal coastal waters such as those of Chesapeake Bay, which impede the accurate characterization of sunrise and sunset, would result in even greater RMS errors. Consequent-ly, light-based geolocation would seem to have limited applicability to short-term PSAT studies of estuarine and coastal fishes.

Habitat-use studies based on PSAT data may benefit from analytical frameworks that incor-porate repeated measures to account for the in-herent within-individual autocorrelation (James et al., 2006; McMahon et al., 2007). Diel differ-ences were not evident in depth or temperature use by coastal migrant striped bass during the January–March tag deployment period. Simi-larly, there were no significant differences in depth and temperature use among individuals or deployment days. During winter, the adult striped bass staging in coastal Virginia and North Carolina waters forage heavily on dense schools of Atlantic menhaden (Brevoortia tyran-nus) before traveling into tributaries to spawn (Raney, 1952). The coastal waters of Virginia and North Carolina are fairly shallow and well-mixed, thus the movements of schooling striped bass during our tag deployment duration likely reflect pursuit of prey by a school of predators rather than the selection of preferred depth or temperature ranges by individual striped bass.

Behavioral rhythms in time-series resulting from ul-trasonic telemetry and, more recently, recovered PSATs, are ideally analyzed by fast Fourier methods if all da-ta are recovered (Hartill et al., 2003; Shepard, et al., 2006). Fast Fourier analysis of full depth time-series data streams from three recovered PSATs deployed on striped bass indicate subtle daily, 12-hour, and 8-hour periodicities. Daily periodicities may represent onshore-offshore movements of striped bass schools into shal-lower and deeper waters when they chase menhaden prey, 12-hour periodicities may correspond to ambient diel light regimes, and 8-hour periodicities may indicate subtle tidal or current effects in the use of depth by striped bass. Mid-Atlantic coastal waters and estuar-ies such as Chesapeake Bay feature semidiurnal tides; tidal stage had substantial impact on movements and habitat use of striped bass in Delaware Bay (Tupper and Able, 2000). Alternately, the 8-and 12-hour period-icities observed in the striped bass data may result from a combination of harmonics resulting from behaviors not strictly sinusoidal in character (Chatfield, 1996). Fourier methods should be applied only to full (100%) data streams to avoid inferring direct spectral relation-ships between two adjacent data packets that are in reality separated in time by sections of untransmitted archived data.

We investigated the applicability of a new generation of smaller PSATs for studies of estuarine and coastal fishes and have provided insights into postrelease sur-vival and habitat use of prespawn aggregating adult striped bass in the winter recreational fishery along the coast of Virginia. Results of this study indicate that tag fouling with physical structures, tag damage resulting from interaction with conspecifics, preda-tors, or scavengers, and reduced transmission efficiency due to beaching or entanglement are not major liabili-ties for striped bass. In fact, the potential for reduced transmission efficiency is more than offset by increased probability of tag recovery resulting in complete data retrieval and the opportunity to reuse the tag at a greatly reduced cost. Collectively, the results of this study on striped bass indicate that the new generation of smaller PSATs may prove to be an effective tool for studying the postrelease survival of and habitat use by other estuarine and coastal fishes.

Acknowledgments

The authors would like to thank K. Neill and the crew of the Healthy Grin for all of their efforts to deploy the tags. We thank P. Howey and R. Tolentino (Microwave Telemetry, Inc.) for technical assistance with tags and R. Howey (University of Bath) for developing the soft-

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100

Per

cent

of a

rchi

ved

data

rec

eive

d

Number of days that data were transmitted

Figure 6Cumulative percentage of archived data that are successfully received by the user as a function of the number of days of transmitted data during the 30-d transmission period for the X-tag high-rate archival tags (Microwave Telemetry, Inc.) pro-grammed with Satellite-In-View (SIVTM) technology at Mid-Atlantic latitudes (available from R. P. Howey, 2009, University of Bath, Bath BA2 7AV, UK). Because of the frequency of Argos satellite passes, tags transmitting at higher latitudes will approach asymptotic data recovery more rapidly, and those transmitting at lower latitudes will approach asymptotic data recovery more slowly.


ware for the tag transmission rarefaction curve. This research was funded by the Virginia Marine Resources Commission Saltwater License Fund, project RF08-06. VIMS contribution no. 3018.

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